'Sometime the hating has to stop.'' This is the final sentence of ''The Railway Man,'' by Eric Lomax. The preceding narrative is a detailed account, by a Scottish septuagenarian with a sharp memory, of his torture during World War II - and of his recent, surprising moves toward coming to terms, in a profoundly touching way, with decades of bitterness.

''The traditional POW attitude,'' Mr. Lomax told me, ''as far as one can summarize it, is: 'Don't forget, don't forgive.''' He held aloft, against the sun, an umbrella that his untiringly considerate wife, Patti, had brought out for him as we sat chatting in their rose-filled garden. ''POWs tend to dwell on ... the need for bitterness,'' he adds knowingly.

That was the way he felt into the late 1980s about his experience as a prisoner of war in Japan, despite valued help since 1987 from a unique organization in London, The Medical Foundation for the Care of Victims of Torture. He describes director Helen Bamber as sympathetically and patiently uncovering and bringing ''back into the light'' the ''hidden traces'' of torture.

As recently as 1991, Lomax admits, he still ''had not spoken to a single Japanese person since 1945.... I was not inclined to forgive.''

Now things have changed. ''The difference between Eric today, and Eric even just a few years ago, is quite incredible,'' says Mike Finlason, maker of a moving documentary film called ''Enemy, My Friend?'' about the unprecedented event in 1993 that was catalytic in changing Lomax's perceptions. At that time he met and forgave one of his Japanese torturers.

In the war, Lomax was a Royal Signals officer attached to the 5th Field Regiment, Royal Artillery. He was among the thousands captured by the Japanese at the fall of Singapore.

Sent to work as an engineer in the lower reaches of the infamous Siam-Burma railway, he was one of six POWs held responsible by the Japanese for surreptitiously making and operating a radio, and, in his case, drawing a map. He was subjected to pitiless thuggery and extreme torture followed by a squalid imprisonment he describes as ''the valley of the shadow of death.''

And yet today he can write: ''I [have] proved for myself that remembering is not enough, if it simply hardens hate.''

These resolute words, in fact, were what he said to his wife as they stood in a POW war cemetery in Thailand in 1993. He had returned (accompanied by Mrs. Lomax and Finlason's film crew) to the exact location of his worst experiences. But his purpose was not just to memorialize, or even simply to confront his memories. It was to meet one of his torturers ''face to face in simple good will.''

Nagase Takashi's voice and face had been a persistently haunting ingredient in his terrible nightmares and flashbacks ever since ''the Kanburi radio affair.'' This diminutive Japanese interpreter had been brought from Saigon to question Lomax. If he was not directly responsible for the Scotsman's physical maltreatment, Lomax certainly believed him to have been the worst sort of psychological torturer. When he discovered that Nagase was still alive today, he was torn by a ferocious desire for revenge on this ''instrument of the emperor.''

Lomax and his wife sent for a book they discovered Nagase had written, ''Crosses and Tigers.'' They were determined to find out as much as they could about him, because he claimed to have devoted his postwar life to acts of charity, assuaging his guilt and remorse. He had become a devout Buddhist. He had financed a temple of peace at the River Kwai Bridge. In his small book, he even claimed at one point that he believed he had been ''pardoned.''

As sea gulls screamed above us in the Lomax's garden, Patti said her reaction to this was ''a really cold anger. I had never felt an anger like it.'' She drafted a letter to Nagase.

Nagase's quick reply - which Patti would not at first open ''because it looked like an evil thing to me'' - seemed, once she read it, to be beautiful and sincere. Her anger drained away. And even Lomax himself silently began to wonder if forgiveness might not be ''a real possibility.''

Further letters and telephone calls followed. One thing led to the next. And, now convinced that Nagase was ''totally genuine,'' they at last made the trip to Thailand. They went on, for a second week, to Japan, staying as honored guests in Kurashiki, Nagase's hometown.

''These two very brave old men,'' as Patti calls them, seem to have found an almost instant rapport.

Lomax agrees. They discovered parallel experiences in their postwar lives; interests such as ''papers, writing, documentation,'' and even nightmares in common. ''I have sat on his chair in his house,'' Lomax says, ''he has the same sort of books on his shelves, same titles, quite extraordinary....''

Both Finlason's documentary and Lomax's book point up an astonishing contrast, however, between the two former enemies. Nagase's fervent sorrow for his ''dirty past'' comes over extrovertly with heartfelt, tender conviction. Lomax's utter sincerity is clothed in an undemonstrative restraint and polite formality.

Understanding that the Buddhist Nagase had a fearful need for his forgiveness, Lomax finally wrote and privately read to him a letter. If he could never forget, he wrote, he nevertheless assured him of his ''total forgiveness.'' He also praised Nagase's courage in arguing against militarism (a stand that still places him at odds with many of his doggedly unapologetic countrymen). And he ''suggested'' that Nagase should ''no longer attempt to carry on his own shoulders ... the guilt of the ... Japanese nation....''

Lomax is the kind of hero who doesn't recognize that he is one. But his heroism has shown itself as much in his journey of personal reconciliation and forgiveness (which he carried out in spite of strong professional psychiatric advice to the contrary), as it did when he refused to confess to the ''hateful little interrogator'' he now calls, in his book, his ''blood-brother.''